Browsing by Author "Dr. John A. Heitmann, Committee Member"

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Adhesive Contaminants (Stickies): Characterization and Their Interaction with Papermaking Components During Paper Recycling
(2002-08-19) Huo, Xin; Dr. Martin A. Hubbe, Committee Member; Dr. John A. Heitmann, Committee Member; Dr. Suzanne T. Purrington, Committee Member; Dr. Richard A. Venditti, Committee Co-Chair; Dr. Hou-min Chang, Committee Co-Chair
The effect of individual paper components on the properties of an acrylate pressure-sensitive adhesive (PSA) after laboratory high-consistency pulping was investigated. The adhesive material was quantified by selectively dyeing the adhesive particles followed by image analysis. It was found that some of the components of copy paper have a significant effect on the size and shape of PSA particles formed during pulping. Further, some copy paper components were also found to have a significant effect on the tackiness and deposition of PSA particles after pulping. The stability of micro-stickies is of great concern to papermakers as these materials, when they agglomerate, can deposit on equipment and on the paper product. In order to investigate, the charge demand of an acrylic microsphere adhesive emulsion (a model for micro-stickies), softwood market pulp and different starches were titrated by standard polymer solutions. The effects of fibers, different cationic polymers and salts on the stability of the micro-stickies were investigated. The stability of the micro-stickies in water was evaluated using turbidity and a hemacytometer with microscope. The agglomeration of micro-stickies with Poly-DADMAC occurred mainly via a neutralization mechanism. In contrast, the agglomeration of micro-stickies with cationic starch does not correspond with neutralization mechanism. Both Poly-DADMAC and cationic starch could stabilize the micro-stickies if they were charged to the system in excess. The adhesive emulsion particles have a double layer and both salts and cationic polymers have an effect on the stability of micro-stickies. The stability with respect to salts with different valence obeyed the Shultz-Hardy rule. Both the anionic fibers/fines and micro-stickies compete for the cationic polymer in the system. PSA particles, or stickies, will agglomerate in water with agitation. Under certain conditions, some starches prevent this agglomeration. Both cationic and neutral starches were found to adsorb onto the surface of the negatively charged stickies. This was determined by infra-red spectroscopy, UV/visible spectroscopy, contact angle measurements and charge titration methods. Cationic charge promotes the adsorption of starch onto the surface of stickies and cationic starches adsorbed on the PSA film do not desorb when exposed for 15 minutes to deionized water at room temperature. Fibers compete with stickies for the cationic charge in the system. Over the molecular weight (MW) range studied, MW has no effect on the stabilization of stickies. The cleanliness efficiencies of macro-stickies and micro-stickies in each operational unit of a recycling mill were qualitatively determined. A deposition tester and a solvent extraction technique were used as complementary methods to analyze macro- and micro- stickies, respectively. The primary coarse screen, secondary fine screen, tertiary fine screen, the cleaners and flotation were found to remove macro-stickies. In contrast, the primary fine screen was observed to have a net macro-stickies cleanliness efficiency of 0%. The primary fine screen caused a significant amount of macro-stickies to change into a more "string-like" shape (like fibers). The deflaker was determined to produce a significant amount of micro-stickies.
Colloidal Behavior of Amphoteric Dry Strength Agents
(2004-03-02) Sezaki, Takao; Dr. John A. Heitmann, Committee Member; Dr. Dimitris S. Argyropoulos, Committee Member; Dr. Martin A. Hubbe, Committee Chair
Dry strength additives are essential to produce paper that is strong enough to meet various usage requirements. Recently, amphoteric copolymers have been developed as more effective dry strength agents for addition during the papermaking process. To understand the mechanism of such polyampholytes, the fundamental colloidal behavior of amphoteric polyacrylamide dry strength additives was investigated. The present thesis includes potentiometric titrations, viscometric and turbidimetric measurements, charge analysis using microelectrophoresis and colloidal titration with a streaming current detector, and adsorption of amphoteric polyacryamides onto bleached kraft hardwood fibers. The potentiometric titration results for the polyampholytes were in agreement with the theoretical curves except in a range between pH 4 and 6. The charge analysis showed that the total charge of the amphoteric polyacrylamides depended on pH. The total net charge was reversed at the pH value termed the iso-electric point, where the polyampholytes have no net charge. The iso-electric points determined by the two measurements, microelectrophoresis and streaming current, coincided well, but not with the calculated values. Around the iso-electric point, the turbidity of the polyampholyte solution was maximized, while the viscosity was minimized. In this region of pH, addition of salt led to swelling of the polyampholyte chain conformation, which was an opposite effect from what is seen in simple polyelectrolytes (anti-polyelectrolyte effect). Namely, the turbidity was decreased and the viscosity was increased by addition of salt to the polyampholyte solution around the iso-electric point. A colloidal titration procedure using a streaming current technique was found to be applicable at either pH 3 or 11 in order to determine the concentration of the polyampholytes. The required titration amount for zero charge was found to deviate from a 1:1 stoichiometric relationship, depending on the salt concentration. The adsorption of the amphoteric polyacrylamide dry strength additives onto bleached hardwood fibers was significantly affected by the pH and salt concentration. Also, it was slightly increased with time for adsorption. The stirring rate during adsorption was not a important factor for adsorption. It was found that the polyampholytes with no net charge were also adsorbed on negatively charged fibers. The maximum adsorption of the polyampholytes was achieved around the isoelectric point. This behavior is attributed to a sufficiently low charge density of the polyampholytes around the iso-electric point, which does not allow the polyampholyte chains to lie flat against the charged surfaces because of electrostatic attractions.
Effect of Different Forming Regimes on Retention Aid Programs (PPJ Studies)
(2003-07-10) Tripattharanan, Taweewat; Dr. Martin A. Hubbe, Committee Chair; Dr. John A. Heitmann, Committee Member; Dr. Richard A. Venditti, Committee Member
A new design of equipment called the Positive Pulse Jar (PPJ) was introduced in this study in order to compare the responses of different retention aid systems to hydrodynamic shear forces resulting from different idealized forming regimes. The major advantage of this equipment for this kind of study is the ability to simulate different forming regimes such as simple filtration, pulsation at different frequencies and amplitudes, uniform-shear forming, and a procedure corresponding to the Britt Jar method. Results showed that pulsations could increase the uniformity of paper, not only in the x-y direction, but also in some cases in the z direction as well. Under the conditions that were used for testing, a dual-polymer bridging system showed the greatest improvement in fine particle retention but this effect could be reduced by the application of hydrodynamic shear before dewatering. Following the application of high level of hydrodynamic shear, charge neutralization didn't show fully reversibility, and it was the least effective retention aid system compared with the other systems. Effects of new-designed cone rotor were also studied; making it possible to explore effects due to a well characterized average shear stress throughout the sample volume. For future studies, suggestions have been made to increase the usefulness of the PPJ as a tool in predicting the performance of new retention aid system under different forming conditions.
Environment and Genetic Effects on Wood Quality of Populus
(2005-08-10) Doungpet, Mayuree; Dr. Richard B. Hall, Committee Member; Dr. Myron W. Kelly, Committee Member; Dr. Perry N. Peralta, Committee Member; Dr. John A. Heitmann, Committee Member; Dr. Ilona Peszlen, Committee Chair
The purpose of the research was to investigate wood properties of new poplar clones from three different environments. Specific gravity, density, and anatomical properties were studied. Impacts of the cottonwood leaf beetle (Chrysomela scripta) on wood properties were investigated on two six-year-old clones in the first study. The results indicated that insect defoliation caused moderate to large decreases in annual growth over the first three years. Clones had different specific gravity and density for protected trees and constant values along the radius regardless of beetle attack. Fiber length was not affected by defoliation. Vessel number and diameter were impacted by defoliation and offsetting changes in vessel numbers and diameters partially cancel out changes in vessel area. Ray area was larger for unprotected trees; one clone responded to defoliation by producing more rays; meanwhile, the other produced fewer but larger rays. The second study dealt with wood properties of eight six-year-old Populus deltoides clones of two families grown under stressful site conditions. There were no differences in growth rate between the two families; however, specific gravity was significantly influenced by family and by clone. Fiber length was affected only by clone and radial position and correlated with growth rate. Clonal averages of fiber length were different closer to the bark suggesting that the earliest selection for fiber length should start after four or five years. The third study analyzed wood variation for four-year-old Populus deltoides trees with exceptional specific gravity and growth rate values. There were significant differences among trees in fiber length and vessel area but not in vessel numbers, vessel diameter, and in ray numbers. The age of the cambium significantly affected all wood properties. The fastest growing tree with high specific gravity had the longest fibers, the highest ray numbers but low vessel area, vessel number, and low vessel diameter representing an unusual combination of traits. Results indicate that trees with similar growth rates can have wide variation in vessel area and that exceptionally fast-growth tree can be achieved with low vessel area.
An Enzymatic Fiber Modification Method for Enhancing Tissue Properties
(2006-05-03) Wallace, Jeff Thomas; Dr. Joel J. Pawlak, Committee Chair; Dr. John A. Heitmann, Committee Member; Dr. Dimitris S. Argyropoulos, Committee Member
Retail consumers of tissue products desire the highest softness at the lowest cost. The softness of a product can be broken down into two components, the bulk (i.e. structural) softness and the surface softness. Traditionally papermakers have used a variety of tools, such as refining, beating, chemical addition, etc., to enhance the softness of paper. The use of enzymatic treatment to enhance the softness of paper is less common, but offers a unique way to modify the chemical composition and ultra-structure of the papermaking fibers. Procter and Gamble has developed a patented process for enzymatically modifying and degrading cellulose fibers to produce softer tissue grade paper. The principle of this technology is that by selectively degrading a cellulose fiber, the bulk softness of the resulting fiber structure can be increased. The main goal of my research was to investigate the fundamental interactions of enzymes with cellulosic substrates in order to better understand the commercialized fiber modification process and the potential for new properties and products this technology offers. A duplication of the Procter and Gamble patented technology was carried out in the research labs using different enzyme concentrations and incubation times. From these duplication experiments, it was found that the patent claims could be reproduced in our laboratories. Furthermore, the enzyme dosage and incubation time could be optimized. An investigation into localized fiber degradation produced by the enzymatic treatment of the fibers was carried out. This investigation was broken into three parts and the first part was to characterize enzyme absorption on softwood fibers by investigating the isolation of enzyme activity to fiber defect (notch/kink) areas using microscopic and image analysis techniques. The results along with the patent duplication experiments relates back to how enzymes affect the fibers to create weaker and more compressible fibers as shown by the microscopic and the zero-span tensile strength results. The results proved that notch/dislocation areas of the fiber are more accessible areas for enzymes and degrade. The results also showed that as incubation time increased, the fibers began to break up and fragment at dislocation areas for enzyme concentrations of 0.5% and higher. The second part of the localized fiber modification study was to study enzyme attachment to softwood fibers. This was tested functionally by attempting to first absorb the enzymes onto fibers and then incubate the fibers with untreated fibers. The sheet properties of jointly incubated fibers and separately incubated fibers were compared. The results indicated that enzymes absorb and desorb from the fiber, reattaching and redistributing to other fibers. The third part of this investigation was to study the effect of enzyme treatment on wet fiber flexibility for refined softwood fibers. The effect on wet fiber flexibility relates back to how enzymes affect the compressibility, bending stiffness and modulus of the sheet as a whole, which is important for improving bulk softness. From the results, it can be concluded that enzymatic degradation affects fiber flexibility as a function of incubation time up to 4.5 hours at 0.5% enzyme concentration. Beyond this time flexibility begins to decrease due to fiber length reduction. Also, two other studies are included in the appendices sections of this thesis (Appendices F & G). The first report is a softwood fiber defects quantification and assessment study. This study attempted to create a method to quantify different types of defects (kinks, dislocations, curls, etc.). The second report is a study on pre-enzyme treatment of fibers to introduce fiber defects with Hobart kneading. It was found that Hobart kneading does not create new defects, but does enhance existing defects and also introduces curl and kink into the fiber.